1. Field of the Invention
The present invention relates to physical quantity detection devices and physical quantity detectors.
2. Description of the Related Art
Gauge pressure sensors having a silicon substrate including a diaphragm joined to an upper surface of a glass substrate have been known. In such gauge pressure sensors, a through hole for communicating the pressure of a medium to be measured is provided in the glass substrate. Furthermore, a metal film for soldering a gauge pressure sensor to a metal base is formed on a lower surface (bottom surface) of the glass substrate. It has been shown that the metal film for soldering preferably has a layered structure of different kinds of films, which is less likely to be degraded by sodium ions included in the glass substrate. (See, for example, Japanese Laid-Open Patent Applications No. 2000-241274 and No. 2-272339 and Japanese Laid-Open Examined Patent Application No. 6-76938.)
On the other hand, apart from the above-described gauge pressure sensors, absolute pressure sensors are known that use a physical quantity detection device in which a space hermetically sealed by a glass substrate and a silicon substrate including a diaphragm is formed by joining the silicon substrate to an upper surface of the glass substrate. For example, a Wheatstone bridge circuit using four piezoresistive elements whose resistance values change depending on an applied pressure is formed on the diaphragm.
In such absolute pressure sensors, a lower surface (bottom surface) of the glass substrate of the physical quantity detection device is fixed onto a substrate by an adhesive agent. The thickness of the silicon substrate is, for example, approximately 1 mm, the thickness of the glass substrate is, for example, approximately 1 mm, and the total thickness of the physical quantity detection device is, for example, approximately 2 mm.